1. Field of the Invention
The present invention relates to an ink jet recording method and apparatus for performing recording by ejecting ink droplets onto a recording medium and, more particularly, to an ink jet recording method and apparatus for performing a multi-pass print operation.
2. Related Background Art
In recent years, office equipment such as computers, wordprocessors, and copying machines has widely become popular, and a large number of recording methods for recording apparatuses for this equipment have been developed. An ink jet recording apparatus has excellent features such as an easy high-definition recording operation, a high-speed operation, low noise, and an inexpensive structure.
The ink jet recording apparatus is prepared with various recording modes in addition to a simple one-scan recording mode for the purpose of solving the problem associated with fixing characteristics of an ink on a recording medium such as a paper sheet, an OHP film, or the like, and preventing density nonuniformity inherent to a recording head.
Of these recording modes, a multi-pass print mode for performing recording by scanning a single recording head a plurality of number of times on a single region on a recording medium is popularly used for various purposes.
For example, when a print operation is performed on a recording medium having no ink absorbency or a very low ink absorbency, or when a color recording operation is performed on a recording medium having a low ink absorbency using a plurality of recording heads having different ink colors, an ink overflows on the recording medium, and causes stripe-like nonuniformity (called "beading") or blurring at a boundary between different colors or densities (called "boundary blurring"), thus considerably deteriorating image quality. In order to prevent "beading" or "boundary blurring" caused by the overflowed ink, a so-called thin multi-pass print mode is employed. In this mode, a single scan pattern is thinned in -checkerboard patterns, and a plurality of thinning patterns are recorded a plurality of number of times, thereby finishing an image corresponding to all the recording data.
In this thin multi-pass print mode, it is considered that the following two effects reduce ink overflowing, and prevent "beading" or "boundary blurring".
(1) The ink amount printed in each pass is decreased as compared to that in a one-pass print mode, and ink is absorbed into a recording medium within a short period of time.
(2) The ink is dried during an interval between adjacent passes.
FIG. 25 is a schematic diagram of an ink jet recording apparatus for executing a conventional thin multi-pass print mode. In FIG. 25, a recording head 1 has a plurality of ink ejection orifices, and a plurality of electrothermal converting elements as ejection energy generating elements arranged in correspondence with the ejection orifices. An ejection signal according to recording data is supplied to each electrothermal converting element, and a bubble generated by heat causes a change in state in an ink, thereby ejecting an ink droplet from the corresponding ejection orifice. The apparatus shown in FIG. 25 includes a carriage 2 for holding the recording head, a guide shaft 3, arranged to oppose a recording medium P which is intermittently moved in a direction of an arrow in FIG. 25 (sub scan direction) by a sub scan roller (not shown), for supporting the carriage 2, a carriage belt 4 for reciprocally moving the carriage 2 along the guide shaft 3 (to perform a main scan operation), and a main scan motor 5 for driving the carriage belt. The apparatus also includes a print mode changing means 6 for changing a print mode automatically or in response to a manual switch operation of a user, a thin-print signal forming means 7 for, when the print mode changing means 6 selects the thin multi-pass print mode, forming thin-print signals for executing the thin multi-pass print mode from an input image signal (to be referred to as a print signal hereinafter) S, and a head driving means 8 for driving the recording head 1 according to a signal from the thin-print signal forming means 7. A main scan motor drive signal forming means 9 forms a signal for driving the main scan motor. When the print mode changing means 6 selects the thin multi-pass print mode, the means 9 sequentially generates driving signals corresponding in number to passes. A main scan motor driving means 10 controls the driving operation of the main scan motor 5 according to the signal from the motor drive signal forming means.
In this ink jet recording apparatus, the thin multi-pass print mode is executed as follows. When the print mode changing means 6 selects the thin multi-pass print mode automatically or in response to a manual switch operation by a user, an input image signal shown in FIG. 26A is thinned according to a predetermined thinning pattern (FIG. 26B) by the thin-print signal forming means 7 to be divided into thin-print signals S1 and S2, as shown in FIGS. 26C and 26D. Of these signals, the thin-print signal S1 is supplied to the head driving means 8 to drive the recording head 1, and ink droplets are ejected from the ejection orifices of the recording head 1. In synchronism with this head driving operation (in practice, a required minimum pass interval before the head driving operation), the main scan motor drive signal forming means 9 generates a main scan drive signal for the carriage, and the main scan motor 5 is driven according to a signal from the driving means. Thus, the carriage 2 is moved along the guide shaft 3 to perform the first-pass print operation. Upon completion of the print operation, the main scan motor 5 is driven in the reverse direction, and the carriage 2 is returned to the start position. The remaining thin-print signal S2 is then supplied to the head driving means 8 to drive the recording head 1, and the second-pass print operation is performed in the same manner as in the first pass. Thereafter, the apparatus prepares for the print operation of the next line.
During this interval, since the sub scan roller (not shown) is controlled not to move the recording medium P, the thin two-pass print operation can be realized. The thin two-pass print operation has been described. However, the same applies to multi-pass print modes using three or more passes.
Upon execution of the above-mentioned thin multi-pass print operation, in order to prevent an ink from overflowing on the recording medium, the number of times of multi-pass print operations is set to prevent "blurring" when a print operation is performed on the recording medium at the possibly highest ink density in an environment with the lowest ink drying speed among possible use environmental conditions. In addition, in order to prevent a decrease in throughput, the interval between the first and second passes (to be referred to as a multi-pass interval hereinafter) is set so that the print operation is started as soon as data are prepared.
For this reason, in order to output an image free from defects such as "beading", "boundary blurring", and the like, the number of times of passes is set to be very large, and this results in promotion of a mechanical wear of sliding portions, an increase in dust attachment frequency of the recording head, a complex electrical circuit for forming thinning data, and the like. Thus, an inexpensive ink jet recording apparatus which can output a high-quality image, and has high durability and reliability, cannot be constituted.